Does New Date for Neanderthal Extinction Mean the End of Human-Neanderthal Interbreeding?
Jim Morrison, iconic lead singer of The Doors, died July 3, 1971 at age 27. Yet conflicting accounts of the cause and location have left a shroud of mystery over his death. Forty years later, it is still not clear how Morrison died. Some even insist he faked his own death.
Image credit: https://en.wikipedia.org/wiki/File:Paryż_père-lachaise_morison.JPG
But this controversy pales in comparison to the scientific debate about the cause and timing of Neanderthals’ demise. In fact, some scientists think Neanderthals may still be among us—or at least a few of their genes—given recent work that suggests these creatures interbred with modern humans. (For a discussion of Neanderthal interbreeding, listen to the May 10, 2010 edition of Science News Flash.)
New research by scientists from Great Britain and Russia adds to the intrigue surrounding Neanderthals and their relationship to humans. Based on improved radiocarbon dating techniques, it appears that Neanderthals may have gone extinct earlier than thought.1
Neanderthals appear in the fossil record around 200,000 to 150,000 years ago. These creatures lived in the Middle East, Europe, and western Asia. Many paleoanthropologists believe Neanderthals went extinct around 28,000 to 30,000 years ago. Humans made their way into Europe around 40,000 years ago, meaning humans and Neanderthals coexisted in Europe for perhaps as long as 10,000 years.
Nobody knows what caused Neanderthal extinction. Some researchers believe that humans killed off these hominids; others think humans out competed Neanderthals. And yet another theory posits that Neanderthals may have died off because they lacked the cognitive ability to handle the challenges of living in Europe. (For a summary of the views on the cause of Neanderthals disappearance, watch the below video.)
New Date for Neanderthal Extinction?
As humans made their way into Europe, they would have had to travel through the Caucasus Mountains. Direct radiocarbon dating of Neanderthal remains recovered relatively near the pathway modern humans took is one way researchers can determine if humans encountered Neanderthals.
Based on this methodology, a number of Neanderthal specimens date younger than 36,000 years in age. One of particular interest is a specimen discovered in the Mezmaiskaya Cave, located in the northwestern foothills of the Caucasus Mountains. A rib taken from this Neanderthal dates to 29,000 years in age. This date is used to support the notion that humans and Neanderthals overlapped in Europe for a significant period of time.
Using radiocarbon methods to date samples 30,000 years and older is tricky because most of the carbon-14 in the sample has decayed, making the method susceptible to contamination by younger material. This problem motivated the scientists to refine the methodology. And with their new and improved capabilities, they re-dated the Mezmaiskaya specimen. It turns out that instead of being 29,000 years old, its closer to 40,000 years old. The researchers suspect other Neanderthal remains dated using less-sophisticated radiocarbon methods are likely older as well.
This result indicates that Neanderthals were probably already extinct before humans made their way into Europe. In other words, it is unlikely humans ever encountered Neanderthals in Europe.
Did Neanderthals and Humans Interbreed?
Of course, the earlier extinction of Neanderthals makes it impossible for them to have interbred with humans in Europe. It also raises questions about whether the two species interbred at all.
Some researchers believe they did based on comparisons between the Neanderthal genome and the five human genomes. These investigators examined the average genetic differences between Neanderthal and human genomes, and noted that the former had more in common with non-African than with African representatives.
The simplest way to explain this difference is if there were limited interbreeding between humans and Neanderthals in the eastern portion of the Middle East, roughly 45,000 to 80,000 years ago, just as humans began to migrate around the world. This would explain why non-African populations display what appears to be a 1 to 4 percent genetic contribution from Neanderthals while African people groups have no contribution whatsoever.
It’s still possible, however, that humans and Neanderthals didn’t interbreed at all. The comparison between the genomes of the two is based on an extremely limited number of samples, and the association between human and Neanderthal genomes is statistical. Also it could be that the signatures in the genomes of non-Africans do indeed exist in some African people groups. If so, then this would mean humans and Neanderthals could not have interbred because Africans never had the opportunity to encounter these hominids directly.
The fact that Neanderthals were probably extinct around 40,000 years ago in Europe means that they might have already disappeared in the Middle East before humans began to migrate around the world. If so, then there is no way interbreeding could have taken place.
- Ron Pinhasi et al., “Revised Age of Late Neanderthal Occupation and End of the Middle Paleolithic in the Northern Caucasus,” Proceedings of the National Academy of Sciences, USA 108 (2011): 8611–16.
- Richard E. Green et al., “A Draft Sequence of the Neanderthal Genome,” Science 328 (May 7, 2010): 710–22.